Pachyhynobius shangchengensis has a stout and strong body, with a total length of 150 - 184 mm and snout-vent length 91 - 114.4 mm for males, and a total length of 157-176 mm and snout-vent length 95 - 106 mm for females. The snout is bluntly rounded and slightly protrudes over the lower lip. The nostrils are located near the end of the snout, and the distance between nostrils is equal to or slightly larger than the distance between eyes. There are both developed gular folds and weak labial folds present (Sparreboom 2014). The head length is larger than the head width, with a slight slope from the end of the snout to the top of the head. At the top of the head, there is also a subtle “V” shaped ridge. There is a thin longitudinal groove behind the eye that reaches the neck pleat (Wu 2014).

Pachyhynobius shangchengensis has short forelimbs. When the limbs are adpressed towards each other, the fingers and toes do not meet. The fingers have relative length of III > II > IV > I. When the forelimb is adpressed anteriorly, it extends past the snout by about half of its total length. The hind limbs are short as well, with five toes having a relative length of III > IV > II > V > I (Wu 2014).

Pachyhynobius shangchengensis has 13 costal grooves. The base of the tail is thick and slightly square, but gradually flattens out at the sides. The tip of the tail is blunt. The caudal fin pleats are well developed and start from the front 1/3 of the tail, and the pelvic fin pleats begin at the rear 1/2 of the tail. There is a mastoid at the front of the anal orifice. The skin is smooth (Wu 2014).

When P. shangchengensis larvae are about 7.8 cm in length, the head is 4.6 cm long and the tail is only about 2/5 of its full length. The mouth is blunt, and the lip pleats are more distinct (Wu 2014).

Pachyhynobius shangchengensis is similar to the southern China species Pachytriton labiatus. While both have smooth skin, a stout body, short limbs, high caudal fins and a dark dorsum, P. shangchengensis has a shorter tail at only 65% of the snout-vent length, a uniform grey venter, and a very thick head in adult males. On the other hand, P. labiatus has a tail that is 80% of the snout-vent length, and a blotchy venter (Sparreboom 2014).

In life, P. shangchengensis is dark brown. The side of the body is slightly lighter, and the ventral surface ranges from a grayish brown to a grayish white. The back and limbs are covered with white star-shaped spots (Wu 2014).

Shortly after metamorphosis, juveniles are black with intense blue dots all over the body in life (Pasmans et al. 2012, Sparreboom 2014). Subadults of P. shangchengensis have a distinct white dorsal pattern and smaller body (Xiong et al. 2007).

Adult males have very thick, broad heads, and can give fierce bites. At time of description, the cause for their strong bites was not known (Pasmans et al. 2012).

Pachyhynobius shangchengensis is found in the Dabie Mountain region of Henan, western Anhui, southeastern Hubei of China. It resides in mountain streams at an altitude ranging from 380 to 1100 m, but is largely restricted to above 500 m. Due to unfavorable environmental conditions at lower altitudes on the mountains, P. shangchengensis populations are isolated from each other on “sky islands”. Each population is found in small pools along these high-altitude streams, where water is cool, slow, and rich in oxygen (Pan et al. 2014). The bottom of these streams are mostly sandstone (Wu 2014).

Life History, Abundance, Activity, and Special Behaviors

Pachyhynobius shangchengensis is mostly nocturnal and hibernates from mid November to March, when water temperature drops below 10°C (Wu 2014). When startled, adult salamanders hide in the cracks of the rocks. When rocks are flipped, they try to blend into the sand (Sparreboom 2014).

Based on one known occurrence of breeding, the female salamander lays a pair of egg sacs of 32 eggs each. The sacs are a dull white, marked with a bluish sheen, and are attached to the undersides of flat stones. The eggs themselves are white and about 3.3 mm in diameter. They are striated and compact with blunt ends. After 42 days, the larvae hatch, and they metamorphose after a year (between 441 and 445 days) when P. shangchengensis is at a length of about 9 cm. Shortly after metamorphosis, juveniles generally live in the water (Pasmans et al. 2012).

Pachyhynobius shangchengensis generally feeds on small insects and their larvae, shrimp, small fish, and other small animals (Wu 2014). Most of these organisms are aquatic invertebrates and cohabit the same streams as P. shangchengensis. In addition, males have fierce bites, the purpose of which was unknown at time of description (Pan et al. 2014).

Pachyhynobius shangchengensis is collected for human consumption and sometimes sold by locals in the pet trade. Its larvae is sometimes sold as Andrias davidianus larvae, which has a high commercial value (Pan et al. 2014).

The species was imported to Europe through the pet trade. Currently, they have been successfully bred on just one occasion, by being kept in large tanks in water temperature below 20°C (Sparreboom 2014).

Phylogenetic relationships were determined using Bayesian inference on 786 base pairs of the mitochondrial DNA control region. Mitogenomic data, implies that P. shangchengensis, the only species of its genus thus known, is the sister taxon to all other hynobiids, except Onychodactylus fischeri. Pachyhynobius shangchengensis might also be the sister taxon to a clade including Batrachuperus, Liua, Pseudohynobius, Salamandrella and Hynobius (Sparreboom 2014).

“Pachy” means stout and fat. The species epithet, “shangchengengensis” takes after Shangcheng, the county where the salamander is found (Sparreboom 2014).

Previously, the subadult P. shangchengensis was thought to be its own species, Hynobius yunanicus, due its distinct white dorsal pattern and smaller body. The two species are now considered synonymous (Xiong et al. 2007). P. shangchengensis is also synonymous with Xenobius melanonychus and Sinobus melanonychus (Frost 2018).